Organic photorefractive materials

About: Organic photorefractive materials is a research topic. Over the lifetime, 697 publications have been published within this topic receiving 13041 citations.

Holographic grating oscillations in photorefractive materials

Abstract: tween interacting beams at the initial stage of their coupling in the case ofthe drift-type nonlinearity.' We have experimentally observed that such a transient coupling is enough to create the mutually pumped phase-conjugate mirror in a Bi,,TiO,, crystal. In this work the nonstationary conditions were implemented by applying a rising front ofthe dc electric field to the sample while both pump beams were derived from cw He-Ne lasers at A = 633 nm. Transient fanning effect of the pulse form was observed under these circumstances at smaller (few degrees) angles of scattering. When we adjust the pump-beams incidence so that formation of both fanning gratings coincides both in space and in time, two transient phaseconjugate waves of the pulse form were generated from the opposite crystal's end faces. Both the response time and the conversion efficiency of transient MPPC depend on the applied electric field as shown in Fig. 1. The curve (a) shows that the higher electric field is applied to the crystal the faster MPPC response time is observed. This contradicts usual behavior of photorefractive media, where the response time grows up with the increasing electric field. However, we have reported recently the anomalous response-time behavior for the fanning effect in a thin Bi,,TiO,, crystal.' It is attributed with the generation of photorefractive surface waves, which appear owing to the internal reflections of fanned beams on the crystal surface and from the photorefractive gratings recorded near this s ~ r f a c e . ~ , ~ As a result, the light energy is self-confined near the crystal surface without any prefabricated waveguide. As fast response time as 4.5 ms was obtained for the external electric field of 61 kV/cm and the pump beam power 10 mW. To the best of our knowledge, this is the fastest MPPC observed in photorefractive crystals under the cw pumping. Note that the conversion efficiency of the transient phase conjugate mirror also grows up while the electric field is increased, as shown in Fig. 1b. Maximal conversion efficiency is measured to be 25%, which corresponds to 39% after the correction to Fresnel reflections.

Photorefractive propery of PMMA-based polymer composites

Abstract: By using Poly(methyl methacrylate) (PMMA) as a host matrix of the materials, we investigate photorefractive property of PMMA-based polymer. The photorefractive index of the materials is experimentally measured by using two-beam coupling method. Because the nonlinear optical molecules, such as phenanthrene quinone (PQ) and azo-dye molecules etc, have been doped with PMMA, the results show that the photorefractive effects are improved evidently. Furthermore we find that the influence of outside electric field on photorefractive property of PMMA-PQ polymer are evidently decreased. The glass transition temperatures of the polymer and the doping amount of chromophore in PMMA are also discussed. Some good results have been obtained.

Photorefractive effect observed in holographic polymer-dispersed liquid crystal film

Abstract: We report on experimental results on two-beam coupling (TBC) that prove the existance of a photorefractive effect of polymer dispersed liquid crystal (PDLC) film.

Constructively and destructively interfering diffraction in a photorefractive medium

Abstract: Diffraction from a photorefractive grating in the presence of two input beams is studied both theoretically and experimentally. The results are extended to the control of the interference of diffracted beams from two photorefractive gratings, which adopts a nondegenerate pulsed wave coupling technique.Keywords: photorefractive effect, grating, optical storage, two-beam coupling, nondegenerate wave mixing,acousto-optic modulation, hologram, angular multiplexing 1. INTRODUCTION The photorefractive effect has attracted much attention since its discovery not only for scientific interests butalso for optical signal processing and image storage1 . In the use of the photorefractive effect for optical signalprocessing or image storage, the typical ways of angular multiplexing of laser beams toward a photorefractivemedium are mechanical methods such as rotating mirrors or a base on which the photorefractive medium sits.Recently, we proved a method of electrical control of the angular multiplexing of mode-locked laser beams towardthe photorefractive crystal by acousto-optic modulation with an external synchronization technique2. That waspossible by enabling nondegenerate wave coupling in a photorefractive medium.In this paper we study diffraction from a photorefractive grating in the presence of two input beams. Generalizeddiffracted beam intensity formulae are suggested. This result could have applications in making a writing-timingschedule ofmany photorefractive gratings.Adopting the technique forming photorefractive gratings with acousto-optically deflected nondegenerate pulsedlasers, we also probe the feasibility of conirolling interferences of diffracted beams from two photorefractive gratings,which could have applications in optical signal processing or optical computing.In section 2, constructively interfering diffraction from a photorefractive grating in the presence of two inputbeams is discussed. In section 3, the control of interference of diffracted beams is discussed adopting a nondegeneratewave coupling technique with acousto-optic angular multiplexing of laser beams.

Optimization of triarylamine photorefractive polymers for high-speed all-optical novelty filters

Abstract: We have demonstrated an optical novelty filter based on the two-beam coupling effect in photorefractive polymers. The photorefractive polymer composition was optimized for response time and two-beam coupling gain by changing the ionization potential and polarizability of various components. In this study, a photorefractive polymer composition was simultaneously optimized for response time and gain, and employed as a key element in a two-beam coupling novelty filter with a high contrast ratio and a limiting frequency of 14Hz, considerably higher than any previously reported in a two-beam coupling photorefractive novelty filter.